Spacecraft such as rockets, shuttles, satellites, orbital stations, and other bodies flying in space are typically outfitted with suitable containers or fuel tanks for storing liquid fuels that are used to power the engines, including engines or thrusters for carrying out apogee maneuvers as well as position regulation in space. In order to drive or propel the liquid fuel out of the fuel tank, the fuel tank is typically also charged with a pressurizing gas or propellant gas, which serves to pressurize the fuel and drive the fuel to the combustion or reaction chambers of the engines. Inert gases such as helium (He) or nitrogen (N2) are typically used as the propellant gases, which are introduced under pressure into the fuel tank, and which thus serve to press the liquid fuel from the fuel tank into the piping system leading to the respective engine. The liquid fuel may be an aggressive storable liquid fuel such as MMH, N2O4, or hydrazine.
With such gas-charged fuel tanks, it is very important to achieve a complete, sure and reliable separation between the propellant gas serving as a conveying medium, and the liquid fuel that is conveyed or delivered to the engine. Namely, when the liquid fuel is delivered to the engine, it is crucial that the liquid fuel must be free of foreign gas inclusions or bubbles at the time of ignition of the fuel. Otherwise, the ignition of the fuel, and the reliable operation of the engine, could be jeopardized.
A fuel tank of the above described general type and operating according to the above described principle is known from the German Patent 100 40 755. Moreover, U.S. Pat. No. 5,293,895 discloses a fuel tank for use in space, whereby the outlet of the tank includes an arrangement of an outlet pipe connected with a reservoir or collection container via a plurality of bored holes.
A standard known method of separating liquids and gases from one another involves the use of screens or sieves, which block the throughflow of gases up to a certain pressure difference across the screen or sieve. Separating devices using such sieves, however, are relatively expensive and complicated. In small satellites with relatively low fuel volume delivery flows, it is possible to avoid the use of such relatively expensive sieves under certain circumstances. Namely, it is desirable to reduce the cost and complexity of the fuel separating arrangements if possible.
A special and often called-for requirement of such tanks is additionally the possibility of transporting the already-filled fuel tank in a horizontal orientation, while the tank is integrated in a satellite, as the satellite is transported to the launch location. This is especially significant, when limitations on the degree of tank filling are to be avoided. Due to dynamic effects, the forces arising during the transport can amount to or exceed a multiple of the forces arising due to normal earth's gravity. In the previously known tanks of this type, it has therefore either been necessary to limit the degree of tank filling in the direction of smaller or partial filling, so that the tank outlet would always be covered or surrounded with liquid, or been necessary to bound the tank outlet by a very narrow or tight channel, which, however, produces relatively high pressure losses when the fuel is withdrawn from the tank during operation. The maximum permissible pressure losses that can occur in that regard are typically prescribed.
A further requirement is the possibility that a satellite equipped with such a tank can be launched into orbit in an orientation perpendicular to the tank outlet. This possibility is especially pertinent for the transport of several small satellites that are arranged laterally horizontally on a central carrier structure. The high dynamic loads that arise during a rocket launch cause any exposed sieves or openings typically to loose their holding or retaining ability, that is to say an entry or penetration of the propellant gas into the outlet cannot be prevented. This leads to a failure if the fuel tank is not completely filled and sensitive components such as sieves and openings protrude out of the liquid. In that case, the propellant gas can penetrate through the sieves and openings to the tank outlet under high load conditions, which similarly lead to a failure of the engine. Therefore, with previously known tanks of the above described type, it has not been possible to carry out a rocket launch with a horizontally oriented tank.